1. Field of the Invention
The invention is directed to methods and materials for tissue reconstruction, repair augmentation and replacement, and particularly to use of such treatments in patients having a defect in urogenital tissues such as the bladder.
2. Description of the Background
The medical community has directed considerable attention and effort to the substitution of defective organs with operationally effective replacements. The replacements have ranged from completely synthetic devices such as artificial hearts to completely natural organs from another mammalian donor. The field of heart transplants has been especially successfully with the use of both synthetic hearts to natural hearts from living donors. Equal success has not been achieved in many other organ fields particularly in the field of bladder reconstruction.
The human urinary bladder is a musculomembranous sac, situated in the anterior part of the pelvic cavity, that serves as a reservoir for urine, which it receives through the ureters and discharges through the urethra. In a human the bladder is found in the pelvis behind the pelvic bone (pubic symphysis) and a drainage tube, called the urethra, that exits to the outside of the body. The bladder, ureters, and urethra are all similarly structured in that they comprise muscular structures lined with a membrane comprising urothelial cells coated with mucus that is impermeable to the normal soluble substances of the urine. The trigone of the bladder, also called the trigonum vesicae, is a smooth triangular portion of the mucous membrane at the base of the bladder. The bladder tissue is elastic and compliant. That is, the bladder changes shape and size according to the amount of urine it contains. A bladder resembles a deflated balloon when empty but becomes somewhat pear-shaped and rises into the abdominal cavity when the amount of urine increases.
The bladder wall has three main layers of tissues: the mucosa, submucosa, and detrusor. The mucosa, comprising urothelial cells, is the innermost layer and is composed of transitional cell epithelium. The submucosa lies immediately beneath the mucosa and its basement membrane. It is composed of blood vessels which supply the mucosa with nutrients and the lymph nodes which aid in the removal of waste products. The detrusor is a layer of smooth muscle cells which expands to store urine and contracts to expel urine.
The bladder is subjected to numerous maladies and injuries which cause deterioration in patients. For example, bladder deterioration may result from infectious diseases, neoplasms and developmental abnormalities. Further, bladder deterioration may also occur as a result of trauma such as, for example, car accidents and sports injury.
Although a large number of bio-materials, including synthetic and naturally-derived polymers, have been employed for tissue reconstruction or augmentation (see, e.g., “Textbook of Tissue Engineering” Eds. Lanza, R., Langer, R., and Chick, W, ACM Press, Colorado (1996) and references cited therein), no material has proven satisfactory for use in bladder reconstruction. For example, synthetic biomaterials such as polyvinyl and gelatin sponges, polytetrafluoroethylene (Teflon) felt, and silastic patches have been relatively unsuccessful, generally due to foreign body reactions (see, e.g., Kudish, H. G., J. Urol. 78:232 (1957); Ashkar, L. and Heller, E., J. Urol. 98:91(1967); Kelami, A. et al., J. Urol. 104:693 (1970)). Other attempts have usually failed due to either mechanical, structural, functional, or biocompatibility problems. Permanent synthetic materials have been associated with mechanical failure and calculus formation.
Naturally-derived materials such as lyophilized dura, deepithelialized bowel segments, and small intestinal submucosa (SIS) have also been proposed for bladder replacement (for a general review, see Mooney, D. et al., “Tissue Engineering: Urogenital System” in “Textbook of Tissue Engineering” Eds. Lanza, R., Langer, R., and Chick, W., ACM Press, Colorado (1996)). However, it has been reported that bladders augmented with dura, peritoneum, placenta and fascia contract over time (Kelami, A. et al., J. Urol. 105:518 (1971)). De-epithelized bowel segments demonstrated an adequate urothelial covering for use in bladder reconstruction, but difficulties remain with either mucosal regrowth, segment fibrosis, or both. It has been shown that de-epithelization of the intestinal segments may lead to mucosal regrowth, whereas removal of the mucosa and submucosa may lead to retraction of the intestinal segment (see, e.g., Atala, A., J. Urol. 156:338 (1996)).
Other problems have been reported with the use of certain gastrointestinal segments for bladder surgery including stone formation, increased mucus production, neoplasia, infection, metabolic disturbances, long term contracture and resorption. These attempts with natural or synthetic materials have shown that bladder tissue, with its specific muscular elastic properties and urothelial permeability functions, cannot be easily replaced.
Due to the multiple complications associated with the use of gastrointestinal segments for bladder reconstruction, investigators have sought alternate solutions. Recent surgical approaches have relied on native urological tissue for reconstruction, including auto-augmentation and ureterocystoplasty. However, auto-augmentation has been associated with disappointing long-term results and ureterocystoplasty is limited to cases in which a dilated ureter is already present. A system of progressive dilation for ureters and bladders has been proposed, however, this has not yet been attempted clinically. Sero-muscular grafts and de-epithelialized bowel segments, either alone or over a native urothelium, have also been attempted. However, graft shrinkage and re-epithelialization of initially de-epithelialized bowel segments has been a recurring problem.
One significant limitation besetting bladder reconstruction is directly related to the availability of donor tissue. The limited availability of bladder tissue prohibits the frequent routine reconstruction of bladder using normal bladder tissue. The bladder tissue that is available, and considered usable, may itself include inherent imperfections and disease. For example, in a patient suffering from bladder cancer, the remaining bladder tissue may be contaminated with metastasis. Accordingly, the patient is predestined to less than perfect bladder function.